package org.apache.lucene.search;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.index.IndexReader;

/**
 * A {@link HitCollector} implementation that collects the top-sorting
 * documents, returning them as a {@link TopFieldDocs}. This is used by {@link
 * IndexSearcher} to implement {@link TopFieldDocs}-based search.
 * 
 * <p>
 * This may be extended, overriding the collect method to, e.g., conditionally
 * invoke <code>super()</code> in order to filter which documents are
 * collected.
 */
public class TopFieldDocCollector extends TopDocCollector {

	private FieldDoc reusableFD;

	/**
	 * Construct to collect a given number of hits.
	 * 
	 * @param reader
	 *            the index to be searched
	 * @param sort
	 *            the sort criteria
	 * @param numHits
	 *            the maximum number of hits to collect
	 */
	public TopFieldDocCollector(IndexReader reader, Sort sort, int numHits)
			throws IOException {
		super(numHits, new FieldSortedHitQueue(reader, sort.fields, numHits));
	}

	// javadoc inherited
	public void collect(int doc, float score) {
		if (score > 0.0f) {
			totalHits++;
			if (reusableFD == null)
				reusableFD = new FieldDoc(doc, score);
			else {
				// Whereas TopDocCollector can skip this if the
				// score is not competitive, we cannot because the
				// comparators in the FieldSortedHitQueue.lessThan
				// aren't in general congruent with "higher score
				// wins"
				reusableFD.score = score;
				reusableFD.doc = doc;
			}
			reusableFD = (FieldDoc) hq.insertWithOverflow(reusableFD);
		}
	}

	// javadoc inherited
	public TopDocs topDocs() {
		FieldSortedHitQueue fshq = (FieldSortedHitQueue) hq;
		ScoreDoc[] scoreDocs = new ScoreDoc[fshq.size()];
		for (int i = fshq.size() - 1; i >= 0; i--)
			// put docs in array
			scoreDocs[i] = fshq.fillFields((FieldDoc) fshq.pop());

		return new TopFieldDocs(totalHits, scoreDocs, fshq.getFields(), fshq
				.getMaxScore());
	}
}
